Voltmeter



(No Model.)

E. R. KNOWLBS.

VOLT METER.

No. 520,789. Patented June 5, 1894.

Vto

UNITED STATES PATENT EDWARD R. KNOWLES, OE MIDDLETOWN, CONNECTICUT, ASSIGNOR TO THE SCHUYLER ELECTRIC COMPANY, OE CONNECTICUT.

VOLTMETER.

SPECIFICATION forming part of Letters Patent No. 520,789, dated June 5, 1894,

Application filed December 5, 14893. Serial No. 492,863. (No model.)

To a/ZZ whom it may concern.-

l 3e it known that I, EDWARD R. KNowLEs, a cltlzen of the United States, residingY at Middletown, in the county of Middlesex and State of Connecticut, have invented certain new and useful Improvements in Voltmeters,`of which the following is a specification.

My invention relates toV instruments for measuring and indicating the voltage of electric currents, or the difference in potential between two conductors of electricity. Its obJ ect is to simplify the construction, cheapen the cost of manufacture, and facilitate the adjustment and repair of the instrument.

My improved volt meter comprises a removable needle of soft iron placed between the poles of a permanent magnet, and inclosed in a shell or tube of copper, to prevent excessive oscillations. A mirror placed under the index enables the readings to be made with greater' accuracy. Other details of construction are hereinafter set forth, and the especially novel features are pointed out in the claims.

In the drawings, Figure 1 is a front elevation of a volt meter embodying my improvements. partly in section. Fig. 3 is a vertical section of a portion of the base showing the push button. Fig 4 is a front elevation of the needle and lndex. Fig.V 5 is a side view thereof. Fig. 6 is an axial section of the copper shell. Fig. 7 is a side view of the cap for said shell, and Fig. 8 shows the needle mounted in the shell.

The apparatus is mounted on a base or back A of insulating material, preferably slate. Firmly secured to the base is a permanent horseshoe magnet B whose poles are fastened to the middle of a non-magnetic spool C, whose axis lies at right angles to the line joining the poles of the' magnet. On this spool are wound the coils C C2, in series, the terminal of one being connected with a binding post D on the base A. The free terminal of the other coil is connected with a resistance coil C8, which is in turn connected through a push button E with the binding post D. The line wires are indicated at Qc, y.

In the middle portion of the spool C, between the poles of the magnet B, is a cylindrical Fig. 2 is a side elevation thereofV socket, in which fits the removable shell Fof copper, provided with a removable cap F. The shell incloses a spindle G, journaled at one end in an adjustable screw bearingfin the inner end of the shell, and at the other end in a central bearing f in the cap F.

The spindle carries ashort wide needle or armature H of soft iron, and an index I, of some light material,preferablyaluminum. A counterweightz' balances the index, which projects through a wide slot f2 in the upper part of the shell, or in the cap.

The scale plate K is preferably supported on a bracket cprojecting from the upper end 0f the spool C. The plate has a slot laconcendle or armature, and turn it till it comes toA rest in the position shown in dotted lines in Fig. 1. The torque tending to return it to this normal position increases with the deflection of the needle fromv this position. The passage of an electric current through the coils C C2 tends to swing the needle to a position parallel with the axis of the spool C, but the torque exerted decreases as the needle approaches that position. When the opposing forces of the magnet and the coils balance each other, the needle comes to rest, and the index points on the scale to the number indicating the voltage of the current. The currents induced by the armature H in the surrounding shell of copper F retard or dampen the movement of the armature, and l thus prevent the index from oscillating so much as to render it difficult to get an accurate reading. The push button enables readings to be taken at will, by merely closing the circuit through the coils C C2. The removable shell F enables the needle and index with the spindle and its bearings to be quickly removed for repairs or adjustment, or to permit other shells containing dierent needles to be inserted.

The Working parts of the instrument are protected by a cover M having a glass top m.

Having thus described my invention, what I claim is 1. In a volt meter, the combination with a permanent magnet, of a spool of non-magnetic material lying transverse to the poles thereof, and containing a socket, and a shell removably iitted into said socket and having journal bearings for an armature spindle, substantially as described.

2. In a volt meter, the combination with a permanent magnet, of a spool of non-magnetic material lying transverse to the poles thereof, and containing a socket, a shell fitted removably into said socket, and a spindle carrying an armature and an index, journaled in bearings in said shell, substantially as described.

3. In a volt meter, the combination with an armature, of a spindle on which it is mounted, and a copper shell surrounding said spindle and having bearings in which the spindle is journaled, substantially asdescribed.

4. In a volt meter, the combination with an armature, of a spindle on which it is mounted, an index on the spindle, and a copper shell surrounding said spindle, having bearings in which the spindle is journaled, and a slot through which the index projects, substantially as described.

In testimony whereof I hereunto set my hand in presence oftwo witnesses.

EDWARD R. KNO WLES.

Witnesses:

D. J. GLAZIER, Jo. T. ELLIOTT. 

